The present invention relates to a thermoplastic composition, to a method for producing a thermoplastic composition, to the thermoplastic composition obtainable by this method, to a method for producing a molded article based on a thermoplastic composition, to a molded article obtainable by this method and also to the use of a mold release agent containing an ester of di- or polyglycerols and at least one carboxylic acid.
Thermoplastic compositions based on thermoplastic polymers are frequently used, on account of their thermoplastic properties, to produce molded articles. This involves heating the thermoplastic compositions to a temperature above the glass transition temperature of the thermoplastic polymers and subsequently injecting them, for example by means of injection molding, into an injection mold which gives the composition its desired shape.
However, effective mold release behavior is a key property for a thermoplastic composition in order to allow efficient and economical processing to form molded articles, for example by means of injection molding. Normally, a mold release agent has to be added to a thermoplastic composition used for producing molded articles in order to allow this processing behavior. In order to effectively function as a mold release agent, an agent of this type or a compound of this type must be stable under the processing conditions, so that it does not lose its effectiveness and/or cause discoloration. Furthermore, if possible, the mold release agent may chemically interact with the polymers and other components of the composition or otherwise adversely affect the composition only to the extent that the properties of the thermoplastic composition are not adversely affected or, if such an effect is inevitable, are affected only slightly. In transparent or translucent polymers, the mold release agent should not impair the transparency. During the injection molding, the mold release agent should not form any deposits on the surface of the mold, nor should it migrate, after molding, into the surface of the part to the extent that it becomes visible on the surface. Such deposition of a mold release agent on the surface of a molded article is referred to as a “tarnish”.
US 2005/0234171 A1 describes a thermoplastic composition which is based on aromatic polycarbonates or mixtures of aromatic polycarbonates and polyesters and contains a mixture of a fatty acid ester of a polyol having 2 to 6 hydroxyl groups and a C10-C36 carboxylic acid and a saturated α-olefin oligomer as a mold release agent. However, the drawback of this thermoplastic composition consists inter alia in the fact that the mold release agent, which is contained therein and consists of two chemically different components (fatty acid ester and α-olefin oligomer) is very complex in its chemical composition. In addition, the transparency of the thermoplastic composition described in US 2005/0234171 A1 is capable of further improvement.
Furthermore, the mold release agents used in the prior art, in particular in US 2005/0234171 A1, display high volatility, causing a part of the mold release agent to escape on account of the high temperatures during the production of molded articles. Not only is this alarming for toxicological reasons; it also leads to an impairment of the detaching behavior of the thermoplastic compositions from the surfaces of an injection mold.